Before taking a photograph, a photographer must first determine the proper combination of the picture, and the camera equipment required to best take that picture, which principally consists in selecting the lens that can best isolate the subject.
The amount of thought and knowledge that a photographer requires to make these decisions varies widely with the type of equipment available and his level of experience. For instance, a beginner with an inexpensive Instamatic type camera sees something he likes, points his camera thereat and snaps the shutter, and generally experiences a low level of success when the photographs are returned from the photo processor, because his lack of training in composition has not taught him to isolate the element that he likes when taking the picture, and the camera design does not allow for lens changes. Needless to say, the present variable angle aperture card will be useless to this type of photographer, as the information provided thereby is incomprehensible.
On the otherhand, there is the serious amateur or professional photographer who understands the basic rule of composition, i.e., how to isolate the essential element of a picture from its surroundings, and who has a camera system available for a given scene, i.e., wide angle, normal, telephoto. This type of photographer has the task of drawing a mental frame around a desired subject, and then, trying to duplicate this mental frame in the view finder of the camera, by changing lenses or camera positions. Often, several lenses must be tried from several positions, which is physically tedious and mentally frustrating to the photographer, and is hard on equipment, since the lens mounts are strained through frequent changing, and camera bodies are opened to dust more often than necessary.
The present variable angle aperture card is specifically designed for this more experienced type of photographer. By so using the same, and without touching his camera and lenses, the photographer may frame the subject with a frame that delimits standard 4".times.5", and other proportionate enlargement sizes and photo dimensions. This indicates what lens must be used from the particular measuring position to take the photograph, and reduces the fumbling and confusion that all photographers encounter, particularly with landscape photography, as well as equipment wear.
It has heretofore been proposed to utilize an open frame as a guide to locate the position for viewing a scene or object to produce the best arrangement, composition, and perspective of a picture to be reproduced therefrom by photography, such as, that shown in U.S. Pat. to Hegel No. 2,669,783. However, in such device, the dimensions of the aperture card are not fixed, but are adjustable, so that the width of the aperture is the baseline, such as the baseline in an isosceles triangle, and this width is changeable, it follows that the distance from the baseline to the apex must also change, if the angle at the apex (angle of view) of the two cotangent sides of the triangle is to remain the same. Accordingly, it is impossible to graduate the longitudinal scale on the slide bar of this prior art device in degrees, in that the changing baseline will cause the actual angle of view to change at a given distance from the apex, as the baseline changed. Therefore, the position of the aperture cannot be correlated with the lens focal length in any camera format, because the angle of view, through the aperture, is the basis for correlation.